Electrochemical sensors are devices that change the electrochemical properties of the material to be changed to electrical signals. Electrochemical sensors are expected to be widely used as biosensors and chemical sensors depending on the kind of target material to be sensed.
For the detection and analysis of a material by an electrochemical sensor, the electrochemical sensor should is required to have high sensitivity so that a great change in the signal thereof can appear even when the target material have fine electrochemical properties. Further, the area of the electrochemical sensor, to which the target material can be attached, is required to be maximized so that a larger amount of the target material can be attached to the electrochemical sensor. In addition, for cost-effectiveness and utility, the electrochemical sensor should be fabricated to have a structure easy to mass-produce.
In such terms, nanowire field effect sensors fabricated using conventional top-down semiconductor processes are most suitable for the above-described requirements of electrochemical sensors. Among them, a nanowire channel is a one-dimensional structure, and has been proposed as a structure that has a high ability to control a gate and that can achieve high sensitivity at a high volume-to-area ratio compared to a flat channel.
To drive the nanowire field effect sensor, a detector material is attached onto the nanowire so that the target material will bind selectively thereto, and sensing is performed based on the charge of the target material. In order to effectively sense the charge of the target material, the area for capturing the target material should be large, and thus the length of the nanowire should be sufficiently long. However, because the nanowire channel is a one-dimensional structure, it is sensitively influenced by traps present in the nanowire and a gate insulating layer covering the nanowire, and thus it is difficult to maintain the difference in properties between the nanowires at a constant level, and this difficulty becomes more severe as the length of the nanowires increases.
In addition, because the nanowires have high channel resistance, the quantity of driving current decreases if the number of the nanowires connected in parallel with one another is small. Thus, when a measurement circuit for sensing is constructed, a high measurement resolution is required.
FIG. 1 illustrates an example of a conventional nanowire sensor comprising a nanowire.
Referring to FIG. 1, in the conventional nanowire sensor, a detector material is attached to a gate insulating layer on a nanowire 20 formed between a source electrode S and a drain electrode D. Next, sensing is performed based on the change in electrical conductivity of the nanowire channel by the charge of a target material which is attached selectively to the detector material. Herein, a separate submerged gate electrode 31 may also be fabricated and used to fix the potential of a solution.
The conventional nanowire sensor has a structure in which the straight nanowire is connected to the source S and the drain D. Herein, the nanowire is constructed as a single layer either attached to the upper surface of a substrate or spaced at a certain distance from the upper surface of the substrate. The sensing area of the nanowire sensor is limited to the upper, lower and side portions of the nanowire, and the size thereof is only a few square microns to a few square nanometers. To increase the sensing area of the nanowires, the number of the nanowires is required to be increased, and the area of elements per substrate area is also increased. This causes a problem in that the number of elements per substrate area decreases.